no iPhone can really be bricked unless you really fuck up. For the future...

1) Plug the phone in to your computer.
2) Turn it off while its plugged in.
3) Hold the POWER button for 10 seconds.
4) Now hold the Home button WITH the Power button for another 5 seconds.
5) Let go of the Power button.
6) Keep on holding Home button for 30 seconds.
Then restore your firmware

3GS's were able to be bricked on newer models produced after September 2011 because apple changed the baseband chip.
If you try to install iPad BB onto the newer 3GS with the new baseband chips, the baseband would be fried and you would lose radio/bluetooth/wifi functions.

Back then, you needed to install iPad BB(6.15.00) on the 3G/3GS in order to unlock the phone if you upgraded after 5.13.04 baseband.